Biometric Sensors Are No Dirtier Than Doorknobs

That was the result from a study by the Biometric Standards, Performance and Assurance Laboratory at Purdue University. Reseachers have found that while the platen glass surfaces of devices that scan fingerprints or hand geometry may look more unsanitary due to visible dirt and prints, they actually harbor about the same amount of bacteria as a normal doorknob.

The study was initiated after participants who were required to touch their hands or fingers to the sensors during fingerprint and hand-geometry studies at the lab voiced their concern about the cleanliness of the touch surfaces.

The researchers tested on three types of biometric sensors: fingerprint, hand-geometry and vein-recognition devices.

Each sensor was tested separately with two kinds of bacteria: Staphylococcus aureus, a common cause of blood and skin infections, and E. coli (Escherichia coli), which can cause diarrhea, urinary tract infections and meningitis. The aim was to find out how well bacteria could survive on these surfaces.

This was how the testing was carried out on biometric devices:

• The surfaces were first sterilized to kill existing bacteria, then coated with a bacteria culture.
• Testers wore sterilized gloves to touch the biometric device surface after 5, 20, 40 and 60 minutes to measure how many of the bacteria were still alive and could be transferred.
• The testers first touched the device surface, then a sterile plate or Petri dish containing growth media to allow any bacteria present to be more easily examined. The solution on the plate was allowed to grow for 24 hours at 37 degrees Celsius (approx. 99 degrees Fahrenheit).
• Next, it was to test for bacterial transfer from the biometric devices. To do this, the devices were sterilized, then testers wearing sterilized gloves touched the device surface and a sterile plate to measure how many bacteria were present before it was contaminated. This was followed by contaminating these surfaces with one species of bacteria at a time, and testers wearing sterilized gloves touched the device surface, then touched a sterile plate containing growth media 50 times. The solution was allowed to grow overnight to quantify the number of live cells recovered from touching the contaminated device.

Researchers found that E. coli survived on the devices slightly longer than staph bacteria, but within 20 minutes, nearly all of the bacteria had died on all three devices.

Following this, a metal doorknob was tested with the same methods and was found that the transfer of bacteria from the doorknob to another surface was nearly identical to that of the biometric devices. On the doorknob, as well as on the three biometric devices, the majority of bacteria was transferred within the first 10 touches.

“What we can take away from this is that no matter what kind of a surface it is, if it is contaminated, the more it is touched, the cleaner the surface becomes,” Christine R. Blomeke, a researcher and doctoral student who was part of the research team said. “Of course, the bacteria are moved to the hand. But it’s important to remember that there are naturally occurring bacteria on everyone’s hands, and hundreds or even thousands of cells would have to enter the body - through a cut in the skin or from mucous tissues - to make a person sick.”

She said that since naturally occurring organisms live on our skin at all times, as well as on frequently touched common surfaces, the fact that some bacteria live on biometric devices shouldn’t deter people from using them.

Source: “Biometric sensors no dirtier than doorknobs, study finds” Purdue University, October 10, 2007

Picture courtesy of Purdue University

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